Chaos is an important research direction in ecology and the number of species in a chaotic state has complex movements in strange attractor. The three species ratio dependent food chain model with Holling Ⅱ functional response was established. The boundedness of species was obtained by differential inequality. The quantitative analysis of the three species food chain model was investigated by numerical simulations and the existence of chaotic dynamic was studied by the bifurcation diagrams. The strange attractor was obtained for suitable choice of parametric values and is existence via double periods. The appearance of chaos in this model suggests that chaotic dynamics may be common in natural food webs.

One of the most interesting topics in ecology systems is the stability of species. The delay population model for a single-species with harvesting was considered. Local stability was given by demark ramification. The curve of population which changes by time was given by numerical simulation, and adequate control of harvesting capacity causes the single-species in stability states.